Valve lifter and forming and processing method therefor

ABSTRACT

A forming and processing method for a valve lifter. The forming and processing method includes the steps of: (a) forming a hole in the valve lifter at a site where a cam is slidably contacted with; (b) forming a diameter-increasing section along an edge of the valve lifter, the edge defining a part of the hole and being located on a side with which the cam is slidably contacted; and (c) carrying out a surface treatment to whole of a surface of the valve lifter which surface is on the side with which the cam is slidably contacted.

BACKGROUND OF THE INVENTION

This invention relates to improvements in a valve lifter in an internal combustion engine, and in a forming and processing method of the valve lifter, and more particularly to improvements in a surface treatment method for a top surface of a crown section or a shim of the valve lifter with which a cam formed to a camshaft is in slidable contact.

In a directly driven type valve lifter of an internal combustion engine, a high frictional resistance is produced between a boss section of a bottom surface of a crown section and a stem end of an intake valve during engine operation. In view of this, a technique as disclosed in Japanese Patent Provisional Publication No. 2001-342810 is proposed, in which a lubricating oil supply hole is formed piercing the crown section of the valve lifter in order to positively supply lubricating oil between the boss section and the stem end.

Additionally, regarding a shim installed to fit in a recess formed at a top surface of the crown section of the valve lifter, some techniques are proposed in which an air hole for blowing air into between a bottom surface of the recess and a bottom surface of the shim is formed piercing the shim. Air is blown through the air hole when the shim is detached from the recess in order to exchange the shim.

Although the lubricating oil supply hole or the air hole is formed on an outer peripheral side of the top surface of the crown section or the shim, a cam formed to a camshaft is in slidable contact with an edge defining the lubricating oil supply hole or the air hole because the cam is in slidable contact with the generally whole top surface in a diametrical direction of the crown section or the shim in order to ensure a high lift amount of the intake valve. Hence, there is a fear that a bearing pressure applied to the edge defining the lubricating oil supply hole or the air hole becomes high when the cam is in slidable contact with the edge.

Therefore, a contrivance to lower the bearing pressure is performed in such a manner that the edge defining the upper end of lubricating oil supply hole or the air hole is chamfered to form a diameter-increasing or flared section.

Moreover, in view of the fact that the cam heavily slides and rotates on the top surface of the crown section or the shim, a surface treatment is carried out on the top surface of the crown section or the shim so that a surface treatment layer high in hardness is formed in order to lower a sliding frictional resistance and to ensure a wear resistance.

SUMMARY OF THE INVENTION

However, regarding the above-mentioned conventional technique in which the surface treatment layer high in hardness is formed on the top surface of the crown section or the shim, the surface treatment layer on the diameter-increasing section is unavoidably thin-walled since the diameter-increasing section is formed along the edge defining the opening of the upper end of the lubricating oil supply hole or the air hole after the surface treatment is carried out.

Accordingly, as shown in FIG. 9, there is a fear that surface treatment layer 23 is partly peeled off from diameter-increasing section 22 a of lubricating oil supply hole 22 under a condition in which the cam is continuously slidable contact with the top surface of disk-shaped shim 21 installed to fit in the recess formed at the top surface of the crown section.

Consequently, wear is liable to occur originating at peeled part 24 of surface treatment layer 23 so as to unavoidably lower durability of the valve lifter.

It is, therefore, an object of the present invention to provide improved valve lifter and forming and processing method therefor which can effectively overcome drawbacks encountered in conventional valve lifters and forming and processing methods therefor.

An aspect of the present invention resides in a forming and processing method for a valve lifter which method comprises the steps of: (a) forming a hole in the valve lifter at a site where a cam is slidably contacted with; (b) forming a diameter-increasing section along an edge of the valve lifter, the edge defining a part of the hole and being located on a side with which the cam is slidably contacted; and (c) carrying out a surface treatment to whole of a surface of the valve lifter which surface is on the side with which the cam is slidably contacted.

Another aspect of the present invention resides in a valve lifter which comprises a crown section formed with a hole at a site where a cam is slidably contacted and having an edge of the valve lifter. The edge defines a part of the hole. A diameter-increasing section is formed along the edge. A skirt section is formed integral with an outer peripheral edge of the crown section. A surface treatment layer is formed on whole of a surface with which the cam is slidably contacted and on an area extending from the diameter-increasing section to inside of the hole.

A further aspect of the present invention resides in a valve lifter which comprises a crown section formed with a circular recess and an oil hole formed to communicate with the recess so as to pierce the crown section. A skirt section is formed integral with an outer peripheral edge of the crown section. A shim is accommodated in the recess and formed with a hole piercing the shim. A diameter-increasing section is formed along an edge defining a part of the hole. A surface treatment layer is formed on whole of a surface with which the cam is slidably contacted and on an area extending from the diameter-increasing section to inside of the hole.

The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a fragmentary cross-sectional view of an essential part of a first embodiment of a valve lifter according to the present invention;

FIG. 2 is a longitudinal sectional view of the valve lifter of FIG. 1;

FIG. 3 is a top plan view of the valve lifter of FIG. 1;

FIG. 4 is a fragmentary cross-sectional view of the essential part of a valve lifter used for an endurance test for the comparison purpose;

FIG. 5 is a cross-sectional view of a valve operating system of an internal combustion engine to which the first embodiment of the valve lifter is applied;

FIG. 6 is a fragmentary cross-sectional view of the essential part of a second embodiment of the valve lifter according to the present invention;

FIG. 7A is a longitudinal sectional view of a valve lifter and a cam under a condition in which they are contacted with each other;

FIG. 7B is a cross-sectional view taken on line A-A of FIG. 7A;

FIG. 8 is a longitudinal sectional view of a fourth embodiment of the valve lifter according to the present invention; and

FIG. 9 is a fragmentary enlarged view of a part around a diameter-increasing section of a valve lifter according to a conventional technique, showing a peeling phenomenon of a diamond-like carbon layer at the diameter-increasing section due to a conventional forming process.

DATAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1 to 3 and 5, a first embodiment of a valve lifter according to the present invention is illustrated by reference numerals 7, 8. Valve lifter 7, 8 form part of a valve operating system of an internal combustion engine for an automotive vehicle.

The valve operating system is shown in FIG. 5 and includes intake and exhaust valves 2, 3 which open or close the open end portions of intake port 1 a and exhaust port 1 b which are communicated with a combustion chamber (not identified) and formed in cylinder head 1. Camshafts 4, 4 provided on intake and exhaust sides are rotatably supported through bearings (not shown) to upper end sections of cylinder head 1. Driving cams 5, 6 are formed integral with the outer peripheral surfaces of camshafts 4, 4. Valve lifters 7, 8 are sliding members which convert rotary motion of driving cams 5, 6 into reciprocating motion and then transfer the reciprocating motion to intake and exhaust valves 2, 3. Valve lifters 7, 8 are slidably held in the inner walls of small diameter bores 1 c, 1 d formed in cylinder head 1, respectively.

Intake and exhaust valves 2, 3 are biased in a direction to close the open end portions of intake port 1 a and exhaust port 1 b respectively by valve springs 12, 13 each of which is elastically disposed between each spring retainer 11 provided to upper end section of each valve stem and the bottom surface of each small diameter bore 1 c, 1 d. Intake and exhaust valves 2, 3 are slidably supported respectively through cylindrical valve guides 9, 10 fixed to cylinder head 1.

Rotational driving force of the engine is transferred to camshafts 4, 4 on the intake and exhaust sides from a crankshaft through a driving sprocket and a driven sprocket which are connected by a timing chain, though not shown. That is, driving cams 5, 6 are rotated together with camshafts 4, 4, thereby pushing or operating intake and exhaust valves 2, 3 in a direction to open the open end portions of intake port 1 a and exhaust port 1 b.

Each of driving cams 5, 6 is formed in a teardrop shape and formed of chilled casting or the like. Cam surfaces 5 a, 6 a formed respectively to the outer peripheral surfaces of driving cams 5, 6 slide on crown surfaces or upper surfaces 14 a of crown sections 14 of valve lifters 7, 8. Additionally, cam surfaces 5 a, 6 a are subjected to super-finishing by polishing, and thereafter subjected to a shot blasting treatment so as to have a certain surface roughness providing a smooth surface.

Regarding valve lifters 7, 8, explanation will be made only on the intake side valve lifter 7 as a matter of convenience. As illustrated in FIGS. 2 and 3, valve lifter 7 is formed of an iron-based metallic material as a one-piece member and includes as the main parts crown section 14 and cylindrical skirt section 15. Crown section 14 is a circular upper wall section. Cylindrical skirt section 15 is formed integral with an outer peripheral edge of crown section 14.

Crown section 14 has crown surface 14 a which is the top surface of crown section 14 and gently spherical or round. In other words, crown surface 14 a is a part of the surface of a large sphere. Crown section 14 includes boss section 14 b which is contacted with a stem end of intake valve 2 and formed in the generally cylindrical shape. Boss section 14 b is located at the central portion of a bottom surface of crown section 14. In order to introduce lubricating oil adhering on crown surface 14 a into the inside of valve lifter 7 through cam surface 5 a of driving cam 5, lubricating oil supply hole 16 is formed at a certain position in a circumferential direction of the valve lifter and on an outer peripheral side of crown section 14 in a manner to pierce crown section 14. In addition, diameter-increasing or flared section 16 a (chamfered section) is formed at an annular portion or edge (of crown section 14) defining the upper open end portion of lubricating oil supply hole 16.

Additionally, surface treatment layer 17 high in hardness is formed on the whole of crown surface 14 a by using a diamond-like carbon treatment. A lapping treatment is made on surface treatment layer 17 after the diamond-like carbon treatment.

Hereinafter, a forming and processing method for the whole of valve lifter 7 will be discussed.

First, an iron-based metal as a base material is formed into a basic shape of valve lifter 7 by cold forging, the basic shape being the shape of a cylinder having a closed bottom.

Then, surface machining is made on the top and bottom surfaces of crown section 14 and the inner and outer peripheral surfaces of skirt section 15. Additionally, machining for forming a hole is carried out at a certain position on the outer peripheral side of crown surface 14 a of crown section 14 so as to form lubricating oil supply hole 16. It will be understood that lubricating oil supply hole 16 may be formed during the above-mentioned cold forging.

Subsequently, valve lifter 7 is subjected to a heat treatment such as carburizing, carbonitriding, nitriding or the like. Thereafter, polishing is made on the outer peripheral surfaces of boss section 14 b and skirt section 15 so as to adjust the outer diameters of boss section 14 b and skirt section 15 to the outer diameter of the stem end and the inner diameter of bore 1 c, 1 d in order to ensure a sliding accuracy.

Subsequently, the whole of crown surface 14 a is subjected to super-finishing so as to have a surface roughness (according to Japanese Industrial Standard JIS B0601) of about 0.1 μm. Additionally, the outer peripheral side of crown surface 14 a is subjected to so-called R-machining (rounding machining) by lapping, barreling, shotblasting and the like so as to have the surface roughness of about 0.2 μm. It will be understood that this surface treatment may be carried out during the above-mentioned polishing. At this time, diameter-increasing or flared section 16 a is formed on the annular portion or edge defining the upper open end portion of lubricating oil supply hole 16, in such a manner that its round surface (in section or a vertical plane containing the axis of lubricating oil supply hole 16) has a radius of curvature R within a range of from about 0.05 to 0.2 mm. Additionally, the surface of diameter-increasing section 16 a is subjected to finishing machining so as to have the surface roughness of about 0.2 μm. This diameter-increasing section 16 a may be formed during the above polishing.

Thereafter, valve lifter 7 is rinsed and then put into an oven for diamond-like carbon treatment. Then, the diamond-like carbon treatment is carried out on the whole of crown surface 14 a so as to form surface treatment layer or diamond-like carbon layer 17 high in hardness on the whole of crown surface 14 a. This diamond-like carbon treatment is carried out not only on the whole of crown surface 14 a but also on the inside surface of lubricating oil supply hole 16 through the surface of diameter-increasing section 16 a of lubricating oil supply hole 16.

Subsequently, brush-lapping is carried out on the surface of surface treatment layer 17, using diamond abrasive grains and a brush, in order to remove a certain amount of microparticles or molecules from the surface of surface treatment layer 17. With this, a plurality of minute recesses are formed at surface treatment layer 17 such that the total area of the minute recesses is about 5 to 30% of the whole area of crown surface 14 a. It will be understood that this surface machining may be replaced with barreling, shotblasting or the like.

For evaluating the durability of the annular portion or edge defining the upper open end portion of lubricating oil supply hole 16 on which surface treatment layer 17 is formed, endurance tests were conducted in such a defining the upper open end portion of lubricating oil supply hole 16 for 100 hours under a condition in which the engine was operated at high speeds. The endurance tests were conducted on a valve lifter (7) of a type wherein lubricating oil supply hole 16 had diameter-increasing section 16 a whose surface was rounded as shown in FIG. 1 and on a valve lifter (7) of a type wherein lubricating oil supply hole 16 had no diameter-increasing section 16 a as shown in FIG. 4. Regarding the valve lifter of the type wherein lubricating oil supply hole 16 has diameter-increasing section 16 a, the radius of curvature R (in section) of the round surface of diameter-increasing section 16 a was varied.

As a result of the tests, with respect to the valve lifter of the type wherein lubricating oil supply hole 16 had no diameter-increasing section 16 a, wear was made at the surface of crown surface 14 a of crown section 14 due to, for example, increasing in bearing pressure.

On the other hand, with respect to the valve lifter of the type wherein lubricating oil supply hole 16 had diameter-increasing section 16 a, little wear was made. Particularly with respect to one having the round surface whose radius of curvature R was within a range of from 0.05 to 0.2 mm, no wear was made. In view of this, it is preferable that the round surface of diameter-increasing section 16 a has a radius of curvature R within a range of from 0.05 to 0.2 mm. With this, the surface treatment layer or film becomes difficult to be peeled off while the bearing pressure can be lowered.

In the first embodiment, since surface treatment layer 17 is formed on the whole of crown surface 14 a by carrying out the diamond-like carbon treatment after diameter-increasing section 16 a having the round surface is formed at the annular portion or edge defining the upper open end portion of lubricating oil supply hole 16, surface treatment layer 17 formed on diameter-increasing section 16 a is prevented from decreasing in thickness. As a result, surface treatment layer 17 on diameter-increasing section 16 a is prevented from peeling-off even if sliding movement of cam surface 5 a is continued, so that a wear resistance of diameter-increasing section 16 a is improved.

Further, since the diamond-like carbon treatment is carried out in an area extending from the whole of crown surface 14 to the inside of lubricating oil supply hole 16, peeling-off of surface treatment layer 17 is sufficiently inhibited even if a shearing force from cam 5 is applied to surface treatment layer 17. Further, in the first embodiment, since diameter-increasing section 16 a is so formed as to have the round surface, i.e., so formed as to have no angular sections, generation of high bearing pressure is suppressed when cam surface 5 a is being slid on valve lifter 7.

Further, in the first embodiment, the minute recesses are so formed that its total area becomes about 5 to 30% of the whole area of crown surface 14 a by lapping after surface treatment layer 17 high in hardness is formed on crown surface 14 a by the diamond-like carbon treatment. With the minute recesses, a frictional resistance between crown surface 14 a and cam surface 5 a can be reduced. Accordingly, a sufficient amount of lubricating oil is always retained in a plurality of minute recesses so that an oil film can be formed between crown surface 14 a and cam surface 5 a when cam surface 5 a is slid on valve lifter 7. Consequently, the wear resistance of valve lifter 7 is improved, while the frictional resistance between crown surface 14 a of valve lifter 7 and cam surface 5 a of cam 5 can be further lowered.

FIG. 6 illustrates a second embodiment of the valve lifter according to the present invention, which is similar to the first embodiment with the exception that diameter-increasing section 16 a at the annular portion or edge defining the upper open end portion of lubricating oil supply hole 16 is formed tapered or having a frustoconical surface in place of the round surface.

Namely, tapered diameter-increasing section 16 a of the second embodiment is shaped into a reversed frustum of a cone having a generally flat surface which is straight in section. The diamond-like carbon treatment is carried out on crown surface 14 a and the surface of the above tapered diameter-increasing section 16 a after tapered diameter-increasing section 16 a is formed.

Therefore, according to the second embodiment, effects as same as those in first embodiment are obtained. Besides, since diameter-increasing section 16 a is formed tapered or frustoconical, its forming and machining is facilitated as compared with those in the first embodiment in which diameter-increasing section 16 a is formed round in section.

FIGS. 7A and 7B illustrate a third embodiment of the valve lifter according to the present invention, which is similar to the first embodiment with the exception that crown surface 14 a of crown section 14 of valve lifter 7 is spherically shaped having a large radius of curvature in section. On this spherical crown surface 14 a, surface treatment layer 17 high in hardness is formed by the diamond-like carbon treatment.

Therefore, according to the third embodiment, since cam surface 5 a is contacted with surface treatment layer 17 in the condition of forming a contact point P, a sliding resistance between them is lowered. Besides, since the normal at the point P can approach an axis X by adjusting an inclination of cam 5 or inclination of the axis of camshaft 4 as shown in FIG. 7B, a sliding resistance between valve lifter 7 and the inner wall of small diameter bores 1 c can be lowered.

FIG. 8 illustrates a fourth embodiment of the valve lifter according to the present invention, which is similar to the first embodiment with the exception that the main body of valve lifter 7 is formed of an aluminum alloy for weight-reduction, in which circular recess 19 is formed at the upper surface of crown section 14, disk-shaped shim 20 being accommodated in circular recess 19.

Oil groove 19 a is annularly formed at a certain position of the outer peripheral side of circular recess 19. Besides, oil hole 19 b through which lubricating oil flows is formed at a certain position in a circumferential direction of oil groove 19 a so as to communicate with oil groove 19 a and pierce the upper wall of crown section 14. Shim 20 is formed of an iron-based metal. Lubricating oil supply hole 16 is formed at a certain position of shim 20 which position corresponds to oil hole 19 b communicating with oil groove 19 a so as to pierce shim 20. Besides, diameter-increasing section 16 a having the round surface is formed at the annular portion or edge defining the upper open end portion of lubricating oil supply hole 16. Moreover, at the top surface of shim 20 on which cam 5 is to be slid, surface treatment layer 17 is formed by the diamond-like carbon treatment. This surface treatment layer 17 is formed by the diamond-like carbon treatment after lubricating oil supply hole 16 and diameter-increasing section 16 a are formed in certain machining processes. Surface treatment layer 17 is formed extending from diameter-increasing section 16 a to the inside of lubricating oil supply hole 16.

Therefore, according to the fourth embodiment, since surface treatment layer 17 is formed after lubricating oil supply hole 16 and diameter-increasing section 16 a are formed, effects as same as those in the first embodiment can be obtained.

The entire contents of Japanese Patent Applications P2004-226230 (filed Aug. 3, 2004) are incorporated herein by reference.

Although the invention has been described above by reference to certain embodiments and examples of the invention, the invention is not limited to the embodiments and examples described above. Modifications and variations of the embodiments and examples described above will occur to those skilled in the art, in light of the above teachings. For example, pierced lubricating oil supply hole 16 of valve lifter may be used as an air hole. The principle of the present invention may be applied to a valve lifter on the side of an exhaust valve. Further, although the diamond-like carbon treatment has been described as being carried out at least after diameter-increasing section 16 a is formed, the forming and machining process is not limited to that described above.

The scope of the invention is defined with reference to the following claims. 

1. A forming and processing method for a valve lifter, comprising the steps of: forming a hole in the valve lifter at a site where a cam is slidably contacted with; forming a diameter-increasing section along an edge of the valve lifter, the edge defining a part of the hole and being located on a side with which the cam is slidably contacted; and carrying out a surface treatment to whole of a surface of the valve lifter which surface is on the side with which the cam is slidably contacted.
 2. A forming and processing method as claimed in claim 1, wherein the surface treatment is carried out in an area extending from the whole of the surface with which the cam is slidably contacted to inside of the hole through the diameter-increasing section formed along the annular edge of the valve lifter.
 3. A forming and processing method as claimed in claims 1, wherein the diameter-increasing section is formed to have a round surface in section.
 4. A forming and processing method as claimed in claim 3, wherein the round surface of the diameter-increasing section has a radius of curvature within a range of from 0.05 to 0.2 mm in section.
 5. A forming and processing method as claimed in claim 1, wherein the diameter-increasing section is formed tapered.
 6. A forming and processing method as claimed in claim 1, wherein the surface treatment is a diamond-like carbon treatment.
 7. A forming and processing method as claimed in claim 6, wherein a lapping treatment is carried out after the diamond-like carbon treatment.
 8. A forming and processing method as claimed in claim 1, wherein a crown surface of the valve lifter is spherically formed.
 9. A forming and processing method as claimed in claim 1, wherein forming the hole is carried out after carrying out a surface processing of a crown section and inner and outer peripheral surface of a skirt section of the valve lifter.
 10. A forming and processing method as claimed in claim 1, wherein the hole is a lubricating oil supply hole and formed during cold forging of the valve lifter.
 11. A forming and processing method as claimed in claim 1, wherein the diameter-increasing section is formed after a heat treatment and a surface polishing which are carried out after the hole is formed.
 12. A forming and processing method as claimed in claim 1, the surface treatment is carried out after rinsing the valve lifter carried out after the diameter-increasing section is formed.
 13. A valve lifter, comprising: a crown section formed with a hole at a site where a cam is slidably contacted and having an edge of the valve lifter, the edge defining a part of the hole, a diameter-increasing section being formed along the edge; a skirt section formed integral with an outer peripheral edge of the crown section; and a surface treatment layer formed on whole of a surface with which the cam is slidably contacted and on an area extending from the diameter-increasing section to inside of the hole.
 14. A valve lifter as claimed in claim 13, wherein the crown section and the skirt section are formed of an iron-based metal.
 15. A valve lifter as claimed in claim 14, wherein a minute recess is formed on the surface treatment layer.
 16. A valve lifter, comprising: a crown section formed with a circular recess and an oil hole formed to communicate with the recess so as to pierce the crown section; a skirt section formed integral with an outer peripheral edge of the crown section; a shim accommodated in the recess and formed with a hole piercing the shim, a diameter-increasing section being formed along an edge defining a part of the hole; and a surface treatment layer formed on whole of a surface with which the cam is slidably contacted and on an area extending from the diameter-increasing section to inside of the hole.
 17. A valve lifter as claimed in claim 16, wherein a minute recess is formed at the surface treatment layer.
 18. A valve lifter as claimed in claim 16, wherein the crown section and the skirt section are formed of an aluminum alloy, and the shim is formed of an iron-based metal.
 19. A valve lifter as claimed in claim 16, an annular oil groove is formed to communicate with inside of the recess, wherein the oil hole is formed to communicate with a first position of the oil groove so as to pierce the crown section, wherein the hole in the shim is formed at a second position corresponding to the oil groove.
 20. A valve lifter as claimed in claim 16, wherein the hole is an air hole through which air flows. 